Let potatoes and mix vegetables cool before handling. Place potatoes, mix vegetables, and eggs in a bowl, and toss. Season with salt and black pepper to taste (remember you can always add more seasoning, so start with about ½ teaspoon salt and ¼ teaspoon black pepper). Add 1-tablespoon mustard to ¾ cup miracle whip salad dressing. Stir until mustard is mixed in with salad dressing, and add to potato mixture. Stir. There are several variations on this potato salad: add diced onions and bell (green) pepper, or cooked macaroni, or canned mix vegetables and/or green peas, or try different salad dressing or mayonnaise.